Determination of the crystalline quality of the piezoelectric materials of class 32 using X-Ray topography

This paper reviews the crystalline quality attained to day by the most important materials of the crystalline class of quartz. Quartz, it-self, can present now a very reduced density of extended defects, however further advances are still possible concerning the impurity content. Aluminum and gallium phosphate crystals were prepared with a low density of extended defects and some times with very low impurity concentrations; however the OH concentration was more rarely very low. Langasite and its analogues can present a quite good crystalline quality but quite often too much defects are still present in the crystals. The interest presented by all the presently known piezoelectric crystals of class 32 for many high-end applications is such that further studies should be made to improve still more their quality.